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Dec. 17, 1929. GERMAN GALLO P 1,740,294

ELECTRICAL CONNECTION Fil-ed VApril 21, 192e ZX j/ WITNESSES INVENTOR Www MW Patented Dec. 17, 1929 UNITED STATES PATENT GFFICE GERMAN GALLO P., OF NEW YORK, N. Y.

ELECTRICAL CONNECTION Application filed April 21,

This invention relates to an electrical connection.

An object of the invention is to provide a simple and efficient construction whereby a high resistance and a low resistance can be connected or joined together without the usual objectionable results.

A further object is t0 provide a construction which is particularly adaptable for high resistance grid leads used in radio sets to avoid the interruption of service in said devices usually due to the fact that the high and low resistance wires are directly connected.

A further object is to provide a construction which is adapted not only for fixed resistanoes but for variable resistances.

The invention is illustrated in the drawings. of which- Figure 1 is a plan view of a variable resistance or grid leak with the spring pressure plate removed;

Figure 2 is a section on the line 2-2 of Figure 1 but showing the spring pressure plate in position;

Figure 3 is section through a fixed re sistance;

Figure 4 is a section on the line 4 4 of Figure 3;

Figure 5 is a diagram illustrating (but not to scale) the normal and the ideal change in conductivity in such a circuit. Figure 6 similarly illustrates the change in accordance with the practical embodiment herein shown.

The form of the invention shown in the drawings is a preferred form, although it is understood that modifications in the construction and arrangement of the parts and in the character of the materials used may be adopted without departing from the spirit of the invention as set forth in the appended claim.-

In the use of resistances, especially high resistances where they have been connected in circuit with low'resistance wires, it has been customary to connect the high resistance portion directly to a low resistance wire or contact and it has been found that when such a direct connection is made that as the surface 1926. serial No. 103,659.

has become corroded and as small or minute arcs are formed that the contact between the two surfaces is so greatly impared that in a very short time the device becomes useless, especially in locations where there is considerable moisture in the air which will facilitate the corroding action.

I have found that these difficulties may be overcome by avoiding the abrupt transition between the high resistance and the low. rl`he type of conductor used in this high resistance has, as is well-known, frequently a value of great magnitude, and the conductivity of the connections as compared with that of the conductor is relatively very high. The diffculty referred to appears to be localized at the juncture point between these substances having such different rates of conductivity. The difiiculty may be overcome by making the transition a more gradual one. Within the broad scope of this invention any means of gradually increasing the conductivity may be employed. For practical purpose I have found that this may be satisfactorily accomplished by interposing between the conductor and the resistance a substance having a conductivity intermediate between the two, so that there will not be such wide discrepancy between the conductivities of adjacent elements. A practical material for this purpose has been found to be the substance sold as fabricoid. The coating of this material is, to normal voltages. substantially an insulator, but as compared with the very high resistance above referred to, it is a conductor. It appears to have a conductivity somewhere a mean between that of the resistance element and of the conductors, so that the transition between the highly conducting and the highly resistaut clement is broken into two commensurate stages. neither one of which is of sufficient magnitude to be so objectionable. In other words the conductivity of the connector between the high and low resistance elements is graded between the conductivity' of these elements and the conductivity in passing from the high resistance element to the low resistance element is gradational.

By making this graded or gradual transition I have found, in practical experience,

that the difficulties and objections hcrcinbefore referred to are eliminated and that it is possible to make a resistance element embodying this principle, which is unusually stable in its resistance value.

In the drawings, which show the preferred form of my invention, I provide a base A10 of insulating material on which I may dispose a strip of material such as paper 11 on which a high resistance line or portion 12 is made. This line may be of inlc or graphite. or of any other suitable substance having a high resistance. At one end of this high resistance line 12 I dispose -a smal-l strip or layer of a material of lower resistance 13 such as fabricoid or any other suitable material I may elect to use. On this layer 13 I dispose a contact strip 14 of metal to which suitable circuit connections may be made in any desired manner. At the other end of the high resistance strip I dispose a 'layer 15 of intermediate resistance value-which may be of fa'hrieoid or other material and on the end of this I dispose a metal contact strip 16. These strips are 4held in place by nuts 17 and 18 and over these is disposed a pressure bar such as 1-9 which may be of any suitable material., this 'bar being in operation held in place by nuts threa-dably disposed on the stems of screws 22 and 23. The layer 15 of intermediate resistance has its free end 24 rolled -u on a stem o-r shaft 25 having a thumb nut-26 whereby it may be manipulated to roll up the free end of the strip 15 either to the lright or unroll it to the left. The flow of current will be for instance from the circuit to the metal strip 16 which is of lo\\"resistance and then through the variable strip 15 of intermediate resistance, through this strip to the high resistance 12 and then along the high resistance '12 to the fixed strip 13 of intermediate resistance and from this to the other contact strip 14 of intermediate resistance. It will be understood that no electrical circuit is provided through the prsure bar 19 and that the elec.- triral circuitis confined to the parts Yjust traced; any well known form of insulation may be provided to prevent passage of any of the current through the bar 19.

'lhis construction therefore inter-poses be.- tn'een each end of the. high resistance and the corresponding low resistance, Contact strips. suit-able layers of material of inter.- mediate resistance .and through which the cur-rent is to pass. In this particular construction the amount of high resistance in circuit is determined by the degree to Vwhich the variable portion of the intermediate re sistnnce is unrolled. The pressure bar 1 9, by pressing on the roll of intermediate resist. ance, will hold it Permanently in any ad.- justed position.

In Figure 3 I show what is preferably a glass tube set 27 having metal caps 28 and 29 on the end thereof to which Contact clips 30 and 31 are fastened. These clips are adapted to embrace the end of a base 32 on which a high resistance element 33 is disposed. At each end and disposed between the high resistance portion and the clips are layers such as 34, 35, 36 and 37 of resistance material of intermediate value. This particular construct-ion is adaptable. for a fixed electrical connection of the type used for fixed grid leaks in radio sets. The values of the high, lo.l and intermediate resistauces can be varied at will and the character of the materials employed may be varied as desired.

It will be understood that such an electrical resistance as here contemplated is intended for use in the oscillatory portions of radio circuits, as for example, for use as a grid leak or as the resistance' element of a resistance coupling. The value of resista-nce employed varies with the use to which it is put.

In Figure 5 is shown the ideal transition between the rate of .conductivity ot the terminals and the rate of conductivity of the high resistance. In this drawing, the ordinates are expressed in rates of conductivity. while the abscissae represent different physical portions of the resistance unit. The extreme right and left hand posit-ions represent the terminals and the central portion represents the resistance element itself. In Figure 5, the straight vertical dotted lines at the terminal with the horizontal dotted intermediate line connecting them, show the customary form of resistance unit with its sudden and instantaneous and extreme change in conductivity. In this same figure, the solid line represents a gradual decrease in conductivity from the terminal to the resistance unit and a. gradual increase on the other end from the unit to the other terminal. This is the ideal situation in which no sudden change of conductivity occurs at any point.

In Figure 6` is shown the practical embodiment ot the invention which is herein illustrated, in which the change between conductivity of the terminal, and conductivity of the resistance element is bridged by the' intermediate resistance, so that instead of one sudden large chamber, there are two smaller ones, resulting in a very great reduction in the resultant diteulties. It would be obvious that the closer the curve may be made to ap.- proach the Contact line of Figure 5, the greater will be the elimination of this source of trouble. The .dotted line represents the present form for comparison, as shown in Fig. 5.

lVhat I claiin isi An electrical resista-nce which comprises a high resistance portion, a portion 0f intel mediate resistance value of variable length contacting therewith and a portion of low resistance value permanently .fixed againstone end of the intermediate resistance portion, means for varying the length of contact of the intermediate resistance With the portion of high resistance, and means for holding the free end of the portion of intermediate resistance irmly against the portion of high resistance.

GERMAN GALLO P. 

